1. Field of the Invention
This invention relates to sulfur-, phosphorus- and molybdenum-containing compositions made from phosphorus-containing acids. More specifically this invention relates to processes for preparing these sulfur-, phosphorus- and molybdenum-containing compositions, which are useful as additives in lubricants. Additionally, this invention relates to concentrates of these compositions and to lubricant compositions comprising these compositions. This invention also relates to methods for reducing fuel consumption by lubricating an internal combustion engine with these lubricating compositions.
2. Description of the Prior Art
Sulfur-containing molybdenum salts of phosphorus-containing acids and processes for preparing said compositions have been described in U.S. Pat. Nos. 3,223,625; 3,256,184; 3,400,140; 3,494,866; 3,840,463, and 4,156,099. These U.S. Patents are hereby incorporated by reference for their disclosures in this regard.
A principal object of the present invention is to provide novel sulfur-, phosphorus- and molybdenum-containing compositions made from phosphorus-containing acids as well as processes for making them.
Another object is to provide novel sulfur-, phosphorus- and molybdenum-containing compositions made from phosphorus-containing acids which exhibit friction reducing properties in lubricants.
Still another object is to provide novel sulfur-, phosphorus- and molybdenum-containing compositions made from phosphorus-containing acids having improved incorporation of molybdenum.
An additional object is to provide novel concentrates comprising these novel sulfur-, phosphorus- and molybdenum-containing compositions.
Another additional object is to provide novel lubricant compositions of these novel, friction-reducing, sulfur-, phosphorus- and molybdenum-containing compositions.
A further object is to provide a novel method for reducing fuel consumption by lubricating an internal combustion engine with these novel, friction-reducing, sulfur-, phosphorus- and molybdenum-containing compositions.
These and other objects of the invention are accomplished by providing a process for preparing a composition which comprises reacting:
(a) A phosphorus-containing acid represented by the formula: ##STR2## wherein each X and X' is independently oxygen or sulfur, each n is zero or one, and each R is independently the same or a different hydrocarbon-based radical; PA1 (b) at least one hexavalent molybdenum oxide compound, and PA1 (c) hydrogen sulfide, PA1 in the presence of PA1 (d) a polar solvent. PA1 1. Dihydrocarbylphosphinodithioic acids, such as amylphosphinodithioic acid, corresponding to the formula, ##STR3## 2. S-hydrocarbyl hydrogen hydrocarbylphosphonotrithioates, such as S-amyl hydrogen amylphosphonotrithioate, corresponding to the formula, ##STR4## 3. O-hydrocarbyl hydrogen hydrocarbylphosphonodithioates, such as O-amyl hydrogen amylphosphonodithioate, corresponding to the formula, ##STR5## 4. S,S-dihydrocarbyl hydrogen phosphorotetrathioates, such as diamyl hydrogen phosphorotetrathioate, corresponding to the formula, ##STR6## 5. O,S-dihydrocarbyl hydrogen phosphorotrithioates, such as O,S-diamyl hydrogen phosphorotrithioate, corresponding to the formula, ##STR7## 6. O,O-dihydrocarbyl hydrogen phosphorodithioates, such as O,O-diamyl hydrogen phosphorodithioate, corresponding to the formula, ##STR8##
Typical phosphorus-containing acids (a) from which the compositions of this invention can be made are known. Illustrative examples of some preferred phosphorus- and sulfur-containing acids are:
Preferred acids of the formula ##STR9## are readily obtainable from the reaction of phosphorus pentasulfide (P.sub.2 S.sub.5) and an alcohol or a phenol. The reaction involves mixing at a temperature of about 20.degree. to about 200.degree. C., 4 moles of the alcohol or a phenol with one mole of phosphorus pentasulfide. Hydrogen sulfide is liberated in this reaction. The oxygen-containing analogs of these acids are conveniently prepared by treating the preferred dithioic acid with water or steam which, in effect, replaces one or both of the sulfur atoms.
Thus, as previously mentioned, the preferred phosphorus-containing acids are phosphorus- and sulfur-containing acids. These preferred acids more preferably include those wherein at least one X is sulfur, more preferably both of X are sulfur; at least one X' is oxygen or sulfur, more preferably both of X' are oxygen and n is 1. Mixtures of acids may be employed according to this invention.
The terminology of "hydrocarbon-based radical" as used herein, ("herein" includes the appended claims) is used to define a substantially saturated monovalent radical derived from a hydrocarbon by removal of a hydrogen from a carbon atom of the hydrocarbon. This carbon atom is directly connected to the remainder of the molecule. These hydrocarbon-based radicals are derived from aliphatic hydrocarbons, cyclo-aliphatic hydrocarbons, aromatic hydrocarbons, mixed aliphatic-cyclo-aliphatic hydrocarbons, mixed aliphatic aromatic hydrocarbons, and mixed cyclo-aliphatic-aromatic hydrocarbons. Therefore, these hydrocarbon-based radicals would be referred to as aliphatic-based radicals, cyclo-aliphatic-based radicals, etc. The base hydrocarbons from which these radicals are derived may contain certain non-reactive or substantially non-reactive polar or non-hydrocarbon substituents.
The terminology "substantially saturated" as used herein is intended to define radicals free from acetylenic unsaturation (--C.tbd.C--) in which there is not more than one ethylenic linkage (--C.dbd.C--) for every 10 carbon-to-carbon (preferably 20) covalent bonds. The so-called "double bonds" in the aromatic ring (e.g., benzene) are not to be considered as contributing to unsaturation with respect to the terminology "substantially saturated". Usually there will be no more than an average of one ethylenic linkage per substantially saturated monovalent radical as described herein. Preferably, (with the exception of aromatic rings) all the carbon-to-carbon bonds in a substantially saturated radical will be saturated linkages; that is, the radical will be free from acetylenic and ethylenic linkages.
In general, the hydrocarbon-based radical may contain up to about 30 carbon atoms with a preferred range of carbon atoms being from one to about 20. The hydrocarbon-based radicals may contain certain non-reactive or substantially non-reactive polar or non-hydrocarbon substituents which do not materially interfere with the reactions or compositions herein, as will be recognized by those skilled in the art. Representative non-hydrocarbon or polar substituents include halo substituents, such as chloro, fluoro, bromo and iodo; nitro; lower alkoxy, such as butoxy and hexyloxy; lower alkyl thio, such as pentylthio and heptylthio; hydroxy; mercapto; ##STR10## and the like. As a general rule, and particularly when the compositions of this invention are to be used as lubricant additives, the degree of substitution and nature of the substituent of the hydrocarbon-based radical is such that the predominantly hydrocarbon character of the radical is not destroyed. Thus, in view of this requirement, these radicals normally have no more than four substituents per radical, and usually, not more than one substituent for every 10 carbon atoms in the radical. Preferably, the hydrocarbon-based radical is a purely hydrocarbyl (i.e., a hydrocarbon radical containing only carbon and hydrogen atoms).
The term "lower" when used herein to denote radicals such as lower alkyl is intended to describe a radical containing up to seven carbon atoms.
Desirable compositions of this invention include those made from phosphorus-containing acids wherein each R is hydrocarbyl, particularly, independently alkyl, aryl, alkaryl and arylalkyl of up to about 30 carbon atoms, more preferably from three to about 20 carbon atoms. The preferred R groups are alkyl and alkaryl, preferably alkyl.
The hexavalent molybdenum oxide compounds (b) useful for this invention are water-soluble hexavalent molybdenum oxide compounds which are acidic under aqueous conditions. The aqueous chemistry of hexavalent molybdenum oxide compounds is well known to those of ordinarily skill in the art and further discussion is not necessary.
These acidic water-soluble hexavalent molybdenum compounds can be obtained from molybdenum trioxide-containing compounds or mixtures of two or more of these compounds.
These molybdenum trioxide-containing compounds include molybdenum trioxide (MoO.sub.3) and compounds that are made from molybdenum trioxide. The molybdenum trioxide-containing compounds include MoO.sub.3, molybdenum trioxide hydrates, molybdic acid, ammonium molybdate, alkali metal molybdates (e.g., sodium or potassium) and heteropolyacid molybdates (e.g., phosphomolybdic acid).
The preferred acidic water-soluble hexavalent molybdenum oxide compounds are molybdenum trioxide; molybdic acid; the heteropolyacid molybdates, especially the phosphomolybdates; those generated by acidification of alkali metal molybdates or ammonium molybdates with, e.g., hydrochloric acid, acetic acid or sulfuric acid; and those generated in an aqueous solution of MoO.sub.3 or its hydrates, wherein the solubility in water of the MoO.sub.3 or its hydrates has been enhanced by the addition of an acid or base.
Also useful as (b) are the hexavalent molybdenum oxyhalides such as MoOCl.sub.4, MoO.sub.2 Cl.sub.2, MoO.sub.2 Br.sub.2, Mo.sub.2 O.sub.3 Cl.sub.6, MoOF.sub.4 and mixtures thereof which can be hydrolyzed by water to the acidic water-soluble hexavalent molybdenum oxide compounds.
A more detailed discussion of the nature of molybdenum trioxide-containing compounds, particularly concerning the description, preparation, acidity and water solubility of these compounds, can be found in D. H. Killeffer and A. Linz, Molybdenum Compounds, Their Chemistry and Technology, Interscience Publishers, New York, 1952, Chapters 4, 6, 7 and 8; and F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, A Comprehensive Text, 2nd Edition, Interscience Publisher-A division of John Wiley and Sons, New York, London, Sidney, 1966, pages 930-960, which are hereby incorporated by reference for their disclosures in this regard.
Normally the hexavalent molybdenum compound (b) or its precursor is dispersed or dissolved in a polar solvent (d). Alternatively, (a) and (b), or their precursors, may be first combined followed by the addition of (d). In some situations it may be desirable to generate (a) and/or (b) in situ, preferably in the presence of (d). In the case of (a), for example, a metal salt of the phosphorus-containing acid (e.g., alkali metal) could be acidified in the presence of (b) to yield (a). In the case of (b), for example, a molybdenum trioxide-containing compound can be used to generate an acidic water-soluble hexavalent molybdenum compound by acidifying an alkali metal molybdate in the presence of (a) and (d) to generate (b) in situ.
For the purpose of this invention it is necessary that a reaction mixture of (a) and (b) is first prepared, preferably in the presence of (d), before reaction with hydrogen sulfide (c).
Hydrogen sulfide (c) is commercially available and can be introduced into the reaction chamber either above or below the surface of the reaction mixture of (a) and (b) in the presence of (d).
Another source can be H.sub.2 S generated in situ. For example, alkali metal sufides, e.g., Na.sub.2 S, could be acidified with HCl to generate in H.sub.2 S in the presence of (a), (b) and (d).
The polar solvent (d) useful for this invention includes water, organic polar solvents such as alcohols, ethers, ketones, and mixtures thereof. The preferred polar solvent (d) is water and mixtures of water and one or more other organic polar solvents. The preferred organic polar solvents are the lower alkyl alcohols, ethers and ketones.
In addition to the polar solvents, the reaction may be carried out in the presence of a substantially inert liquid solvent/diluent medium. This solvent/diluent medium desirably serves to maintain contact of the reactants and facilitate control of the reaction temperatures. Examples of suitable solvent/diluent media include aliphatic and aromatic hydrocarbons as benzene, toluene, naphtha, mineral oil, hexane; chlorinated hydrocarbons as dichlorobenzene and heptylchloride.
As used in the specification and the appended claims, the term "substantially inert" when used to refer to solvents/diluents, and the like, is intended to mean that the solvent/diluent, etc., is sufficiently inert to chemical or physical change under the conditions in which it is used so as not to materially interfere in an adverse manner with the preparation, storage, blending and/or functioning of the compositions, additive, compound, etc., of this invention in the context of its intended use. For example, small amounts of a solvent/diluent, etc. can undergo minimal reaction or degradation without preventing the making and using of the invention as described herein. In other words, such reaction or degradation, while technically discernible, would not be sufficient to deter the practical worker of ordinary skill in the art from making and using the invention for its intended purposes. "Substantially inert" as used herein is, thus, readily understood and appreciated by those of ordinary skill in the art.
As used in the specification and the appended claims, the term "solvent/diluent medium" is intended to include those solvent/media in which independently each of the reactants are soluble or stably dispersible. The term "stably dispersible" as used in the specification and the appended claims is intended to mean a composition (e.g., a single compound, a mixture of two or more compounds, etc.) is capable of being dispersed in a given medium to an extent which allows it to function in its intended manner. Thus, for example, where a composition is prepared by a reaction in an oil, it is sufficient that the reactants be capable of being suspended in the oil in a manner sufficient to allow the reaction to occur and the formation of the composition. Thus, the term "solvent/diluent medium" is understood and can be used in a conventional manner by those of ordinary skill in the art.
The product of reacting components (a), (b) and (c) in the presence of (d) may be used as a lubricant additive, however, it is preferred that (d) be removed particularly when (d) is water. The compositions made by reacting (a), (b) and (c) in the presence of (d) sometimes may be accompanied by the formation of by-products and/or excess solvent/diluent medium which may lessen its commercial appeal. Accordingly, the polar solvent (d), undesirable by-products and/or excess or undesired solvent/diluent medium can be separated from the compositions of this invention by techniques known in the art, e.g., filtration, evaporation (e.g., stripping), etc., to obtain a more desirable product. Alternatively, if the solvent/diluent medium is, for example, a base suitable for use in the lubricating compositions of this invention, the product can be left in the solvent/diluent medium and used to form the lubricating compositions as described below.
A reaction mixture of (a) and (b) must first be prepared before reaction with (c) in the presence of (d). It is preferred that (d) is present when preparing the reaction mixture of (a) and (b); and it is particularly preferred to disperse or dissolve (b) in (d) before contact with (a). This reaction mixture may be conveniently prepared within a temperature range of from about 0.degree. up to about 150.degree. C., preferably from about 25.degree. C. up to about 100.degree. C.
The reaction of (a), (b) and (c) in the presence of (d) may be conveniently carried out at within the temperature range of about 0.degree.-150.degree. C. Although it is not necessary, it is preferred to control the temperature so that it is reasonably constant throughout the course of the reaction, It is particularly preferred to control the temperature within the range of from about 50.degree. C. up to about 100.degree. C.
The period of time for reaction varies with several factors including nature and amount of reactants, reaction equipment, solvent/diluent medium, degree of mixing, and the like.
For the purposes of this invention, the molecular weight of a phosphorus-containing acid (a) is equal to its equivalent weight and, therefore, one mole of (a) is equal to its equivalent weight, which is determined by substituting its "acid number" in the following equation: ##EQU1## The "acid number" is defined as the number of milligrams of KOH used to raise the pH of one gram of sample under aqueous conditions to about 4.0. The pH of about 4.0 can be determined by the use of an indicator that changes color in the range of 3.0 to 4.5 such as bromphenol blue or by electrical means such as a pH-meter.
For the purposes of this invention, the ratio of reactants (a) to (b) is from about 0.5 up to about four moles of the phosphorus-containing acid (a) per mole of molybdenum in (b) (e.g., one mole of Na.sub.2 MoO.sub.4 contains one mole of molybdenum; ammonium paramolybdate, (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 O, contains seven moles of molybdenum). A ratio of at least about 0.5 mole of hydrogen sulfide per mole of molybdenum in the reaction mixture of (a) and (b) is desirable.
Therefore, the range ratios of (a):(b):(c) is from about 0.5 up to about four moles of (a):one mole of molybdenum in (b):at least 0.5 mole of H.sub.2 S. A ratio of about 1:1:1.5 is optimum, although an excess (i.e., 1:1:&gt;1.5) of hydrogen sulfide can be used to insure complete reaction. A ratio of 1:1:4 or more may be used, but a ratio of 1:1:2 should be sufficient to insure complete reaction. Excess hydrogen sulfide can be removed by blowing the reaction mixture with an inert gas such as nitrogen.
The polar solvent (d) is essentially a promotor or contact agent. Therefore, minimum amount of polar solvent (d) is that amount necessary for the reaction of (a), (b) and (c) to proceed (i.e., the point at which the hydrogen sulfide will react with (a) and (b) in the presence of (d)). Generally, enough (d) is used to disperse or, preferably, dissolve the molybdenum trioxide containing compounds or the molybdenum-oxyhalide compounds previously described. Usually from about one up to about four parts of (d) will be used for each part by weight of the above-described molybdenum compound used. Substantial amounts of (d) in excess of this would not be uncommon, but would not be advantageous.
This invention is exemplified in the following examples. Of course, these examples are not intended as limiting this invention as modification of the examples by ordinary expedients will be readily apparent to those of ordinary skill in the art.